Thin film transistor liquid crystal display (TFT-LCD) dominates the display market. According to one technique, the TFT-LCD comprises an array substrate, an opposite substrate and a liquid crystal layer provided between the array substrate and the opposite substrate.
A structure of the opposite substrate is shown in FIG. 1 (a)-FIG. 1 (b). As shown in FIG. 1 (a)-FIG. 1 (b), the opposite substrate comprises a base substrate 141, a black matrix 142, a color filter layer 143 (for example, comprising a red filter unit 143R, a green filter unit 143G, and a blue filter unit 143B), and a columnar spacer 150. The black matrix 142 prevents light leakage between pixels and prevents color mixture so as to increase color purity and color contrast.
A structure of the array substrate (i.e. TFT substrate) is shown in FIG. 2. As shown in FIG. 2, the array substrate comprises a base substrate 111, and a plurality of gate lines and a plurality of data lines formed on the base substrate 111. The plurality of gate lines and the plurality of data lines intersect with each other to define a plurality of pixel units. Each pixel unit comprises a pixel electrode 130 and a thin film transistor. The thin film transistor comprises a gate electrode 112, a gate insulation layer 113, an active layer, a source electrode 116 and a drain electrode 117 that are formed on the base substrate 111. The active layer comprises a semiconductor layer 114 and a doped semiconductor layer 115. The array substrate further comprises a transparent protection layer 118, and the pixel electrode 130 is connected with the drain electrode 117 through a via hole 119 penetrating through the transparent protection layer 118.
The array substrate and the opposite substrate are bonded with each other, and the black matrix on the opposite substrate covers the gate line, the data line and the thin film transistor on the array substrate. Light leakage may occur at an edge of the pixel unit due to misalignment of the array substrate and the opposite substrate. Thus, the black matrix has to be widened, which however results in a decrease of the aperture ratio.